Theoretical study of new 3-(methylthio)-8-phenyl-8H-thieno[2,3-b]indole derivatives for application in DSSC: Solvent effect, adsorption process on the surface of TiO2

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This investigation aims to elucidate the influence of chemical modifications of the π-bridge on the optoelectronic properties of a newly designed series of five dyes Di (i = 1–5). In this regard, the molecules are designed with 3-(methylthio)-8-phenyl-8H-thieno[2,3-b] indole as electron-donating fragments and cyanoacrylic acid as electron-accepting groups. To attain this goal, the optoelectronic properties of the Di dyes and the reference dye MKZ-39 were theoretically investigated in both the gas phase (GP) and Toluene solvent (TS) using Density Functional Theory (DFT). In addition, to predict the absorption spectrum and excited state properties of theoretical Di molecules, we have resorted to Time-dependent Density Functional theory (TD-DFT). Furthermore, the Monte Carlo approach was employed to theoretically evaluate the process of dye adsorption onto the surface of TiO2 (110) anatase to determine the most stable TiO2-dye-100 C7H8 complex. The results presented demonstrate that the selected dyes possess auspicious characteristics as potential promoters for solar cells, including a redshift of λMax that can reach 561 nm, a nearly complete Light-Harvesting Efficiency (LHE) of 99 %, and a higher open-circuit voltage (VOC) compared to the reference molecule. Our results could open new perspectives for further experimental research into the chemical-structural modifications of these sensitizers.